diff --git a/phpseclib/Net/SFTP.php b/phpseclib/Net/SFTP.php
index e139be53..f87a0aee 100644
--- a/phpseclib/Net/SFTP.php
+++ b/phpseclib/Net/SFTP.php
@@ -1876,10 +1876,12 @@ class SFTP extends SSH2
 
             if ($local_start >= 0) {
                 fseek($fp, $local_start);
+                $size-= $local_start;
             } elseif ($mode & self::RESUME_START) {
                 // do nothing
             } else {
                 fseek($fp, $offset);
+                $size-= $offset;
             }
         } elseif ($dataCallback) {
             $size = 0;
diff --git a/tests/Functional/Net/SFTPUserStoryTest.php b/tests/Functional/Net/SFTPUserStoryTest.php
index 6539c675..6e607c30 100644
--- a/tests/Functional/Net/SFTPUserStoryTest.php
+++ b/tests/Functional/Net/SFTPUserStoryTest.php
@@ -651,5 +651,22 @@ class Functional_Net_SFTPUserStoryTest extends PhpseclibFunctionalTestCase
         $this->assertSame($stat['type'], NET_SFTP_TYPE_SYMLINK);
 
         $sftp->enableStatCache();
+
+        return $sftp;
+    }
+
+    /**
+     * @depends testStatVsLstat
+     * @group github830
+     */
+    public function testEndlessLoopOnUpload($sftp)
+    {
+        $sftp->put('endless.txt', 'res.txt', SFTP::SOURCE_LOCAL_FILE, 0, 10);
+
+        $this->assertSame(
+            substr(self::$exampleData, 10),
+            $sftp->get('endless.txt'),
+            'Failed asserting that portions of a file could be uploaded.'
+        );
     }
 }